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From: awb@uk.ac.ed.aipna (Alan W Black)
Newsgroups: comp.os.minix
Subject: Re: test/[ solved; new question: executable scripts?
Message-ID: <AWB.91Apr30101536@stoat.uk.ac.ed.aipna>
Date: 30 Apr 91 10:15:36 GMT
References: <1991Apr29.110459.25477@doe.utoronto.ca> <9818@star.cs.vu.nl>
Sender: news@aipna.ed.ac.uk
Organization: Dept of AI, Edinburgh University, UK
Lines: 46
In-reply-to: jms@cs.vu.nl's message of 29 Apr 91 22:45:45 GMT


In article <9818@star.cs.vu.nl> jms@cs.vu.nl (Jan-Mark) writes:

   #> [ other stuff deleted ]
   #>
   #> I am also interested in executable scripts. Right now, when I make a
   #> script executable, the kernel always seems to presume that it is for
   #> sh. I would like to have executable scripts like
   #> 
   #> 	#!	/usr/gnu/bin/gawk
   #> 
   #> 	BEGIN { print "hello" }
   #> 
   #> 	/bug/ { print "Oh no!" }
   #> 
   #> 	END { print "bye" }
   #> 
   #> If this script were called "buggy", and I chmod'd it to make it
   #> executable, I would expect it to run under gawk, but the kernel still
   #> gives it to sh (can't find BEGIN...). Any advice, or is this another
   #> incredible dumb question?

	   To some kernels #! is a magicnumber. If a file has #! as first
	   two bytes, the rest of the line is put into an array and used 
	   in an ``system ()'' call. So hack the kernel is you want this!
	   But are you sure you DO want this, remember; small is .....

	   Jan-Mark.

				    (:>	jms
				   (_)
			   ========""======

The gnu shell Bash actually checks for #! in the file it is about to
execute so this technique does work when using bash (available on
request).  This surprised me as I thought Minix wouldn't do this but
then realised that I has been using #! in my shell scripts for ages
and it always worked.  On investigation I saw that bash could deal
with this itself without any kernel change.  (I'm sure this is
the right thing for bash to do though :-)

Alan

Alan W Black                          80 South Bridge, Edinburgh, UK
Dept of Artificial Intelligence       tel: (+44) -31 650 2713
University of Edinburgh               email: awb@ed.ac.uk